CCD image sensors, in general, comprise a substrate of a semiconductor material having therein a plurality of photodetectors, such as photodiodes, arranged in an array of rows and columns, and a separate vertical CCD shift register extending along each column of the photodetectors. A horizontal CCD shift register extends across and is electrically connected to one end of each of the vertical CCD shift registers. Each of the vertical CCD shift registers includes a channel region in the substrate extending between and parallel to the columns of the photodetectors and conductive gates along and extending across the channel regions substantially parallel to the rows of the photodetectors. Each photodetector forms a pixel of the image sensor.
In the operation of the image sensor, the photodetectors receive illumination from the image being sensed during a scene integration period and convert the illumination to charge carriers which are temporally stored in the photodetectors. When the gates of the vertical CCD shift registers are properly pulsed, the charge carriers are transferred from the photodetectors to a channel region of the vertical CCD shift registers. Then by appropriately pulsing the gates, the charge carriers are transferred along the channel regions of the vertical CCD shift registers to the horizontal CCD shift register which carries the charge carriers to an output circuit.
For various uses of the image sensor, the vertical CCD shift registers are operated in either an interlace mode or a non-interlace mode. In the interlace mode, during the transfer period, the gates for a first set of alternating photodetectors in each column, such as the odd numbered photodetectors, are pulsed at one time to transfer the charge carriers from the odd numbered photodetectors to the channel region of the vertical CCD shift register. These charge carriers are then transferred along the vertical CCD shift registers to the horizontal CCD shift register. Then the gates for the other set of alternating photodetectors in each column, such as the even numbered photodetectors, are pulsed to transfer the charge carriers from the even numbered photodetectors to the channel regions of the vertical CCD shift registers. These charge carriers are then transferred along the vertical CCD shift registers to the horizontal CCD shift register. One major use of the interlace mode is in a camera for television since it is compatible with television operation.
In the non-interlace mode, the gates for all of the photodetectors in each column are pulsed at the same time. This results in the charge carriers for all of the photodetectors in each column being transferred at the same time to the channel regions of the vertical CCD shift registers. All of the charge carriers are then transferred to the horizontal CCD shift register. This mode provides a higher resolution of the image sensed and is used in still cameras and the like.
In order to have a CCD image sensor which is highly flexible and can be used for various purposes, it is desirable to have an image sensor which can be operated in either the interlace mode or the non-interlace mode. So far attempts to make such an image sensor have not been completely satisfactory. For example, U.S. Pat. No. 4,816,916 (I. Akiyama, issued Mar. 28, 1989), entitled "CCD Area Image Sensor Operable in Both of Line-Sequential and Interlace Scannings and a Method for Operating the Same" describes an image sensor which includes additional storage regions and electrodes to allow operation in both modes. This makes the image sensor more complex and therefore more expensive to manufacture. U.S. Pat. No. 4,805,026 (E. Oda, issued Feb. 14, 1989), entitled "Method for Driving a CCD Area Image Sensor in a Non-interlace Scanning and a Structure of the CCD Area Image Sensor for Driving in the Same Method" and the pending application for U.S. patent application Ser. No. 478,857 (D. L. Losee et al., filed Feb. 12, 1990), entitled "Selective Operation in Interlaced and Non-interlaced Modes of Interline Transfer CCD Image Sensing Device", each describe a method of a CCD image sensor in either interlace or non-interlace mode. However, these devices require extra gate electrodes and clock drivers as well as special clocking of the gates of the CCD shift registers and special circuits to carry out the clocking. Therefore, it would be desirable to have a CCD image sensor that has a relatively simple structure and can be operated in either interlace or non-interlace mode without special clocking circuits and which is of simple construction.